Although not exclusively, the present invention particularly applies to the military field, i.e. to the situation where two military airplanes are to meet for refueling one by the other.
It is known that, generally, refueling successively comprises the following phases:                a waiting phase, during which the refueling aircraft is in the air on a waiting circuit waiting for the receiving aircraft;        a meeting phase, during which the two aircrafts are positioned in order to be able to carry out refueling; and        a refueling phase as such, during which the two aircrafts fly along a refueling circuit implementing said refueling.        
When the receiving aircraft is on the way for the refueling circuit, it takes a contact, via radio, with the refueling aircraft for coordinating their positions. The refueling aircraft then leaves the waiting circuit for reaching the receiving aircraft upon the meeting phase.
The procedures to be implemented during the meeting phase are accurately defined in a document published by the NATO (North Atlantic Treaty Organization). This document referred to as ATP56(B) dated 1 Apr. 2007 defines the standards and the international regulations for perfectly implementing in a safe way the meeting and in-flight refueling procedures. For this, the NATO has defined several types of in-flight meeting procedures, i.e.:                a meeting of the A type (referred to as ALPHA);        a meeting of the B type (referred to as BRAVO);        a meeting of the C type (referred to as CHARLIE);        a meeting of the D type (referred to as DELTA);        a meeting of the E type (referred to as ECHO);        a meeting of the F type (referred to as FOX-TROT);        a meeting of the G type (referred to as GOLF).        
Using such procedures depends on the operational context (conflict, training, etc.), on the equipment on board the aircrafts, as well as their accuracy. The B, C and D type procedures are implemented in a completely autonomous way by both aircrafts, that is to say that no means being external to these two aircrafts interferes in the progress of the meeting phase. More precisely:                a B type procedure suggests that the two aircrafts face each other on a same trajectory, and at a predetermined engaging distance, the refueling aircraft starts a turn with respect to its initial heading at a constant angle of turn, for performing a half-turn, whereas the receiving aircraft remains on its trajectory;        a C type procedure suggests that the two aircrafts face each other on one single trajectory and at a predetermined engagement distance, the refueling aircraft starts a turn with respect to its initial heading at a constant angle of turn. The receiving airplane also starts a turn in order to be laterally shifted and be on the same (new) trajectory and in the same direction as the refueling aircraft; and        a D type procedure suggest that the two aircrafts face each other, but are laterally shifted by a predetermined lateral distance. At a predetermined engagement distance, the refueling aircraft starts a turn with respect to its initial heading, whereas the receiving aircraft remains on its trajectory.        
The three B, C and D type procedures require from the refueling aircraft that it accurately observes the relative distance with respect to the receiving aircraft, in order to start a final turn exactly at the predetermined corresponding engagement distance, in order to initiate the meeting phase. At the end of the meeting phase, the two aircrafts integrate the refueling circuit and implement the refueling operation as such.